Climate change skeptics/common claims and rebuttal

This Climate change skeptics/common claims and rebuttal page offers some arguments and rebuttals; other, likely more up-to-date compendia are in the "External resources" section below.

Confusion effort
A 2007 report from the Union of Concerned Scientists found that ExxonMobil has funneled nearly $16 million between 1998 and 2005 to a network of 43 manmade global warming skeptic groups to confuse the public on global warming science.

Arguments and rebuttals
The following are arguments commonly used or cited by global warming skeptics, followed by respective scientific rebuttals.

Skeptic Assertion
An internal 1995 document (pdf) of the Global Climate Coalition (GCC) -- an industry front group that disbanded in 2002 -- reviewed some of the "contrarian" arguments used by Richard Lindzen and other climate change skeptics. The document was obtained as part of a court action against the automobile industry.

In a section on the "Role of Water Vapor", the GCC's Science and Technical Advisory Committee wrote that "In 1990, Prof Richard Lindzen of MIT argued that the models which were being used to predict greenhouse warming were incorrect because they predicted an increase in water vapor at all levels of the troposphere. Since water vapor is a greenhouse gas, the models predict warming at all levels of the troposphere. However, warming should create convective turbulence, which would lead to more condensation of water vapor (i.e. more rain) and both drying and cooling of the troposphere above 5 km. This negative feedback would act as, a "thermostat" keeping temperatures from rising significantly."

Rebuttal
However, the GCC's own science advisers noted in 1995 that this argument had been discounted to the point that Lindzen himself had ceased to use it. "Lindzen's 1990 theory predicted that warmer conditions at.the surface would lead to cooler, drier conditions at the top of the troposphere. Studies of the behavior of the troposphere in the tropics fail to find the cooling and drying Lindzen predicted. More recent publications have indicated the possibility that Lindzen's hypothesis may be correct, but the evidence is still weak. While Lindzen remains a critic of climate modeling efforts, his latest publications do not include the convective turbulence argument."

In conclusion the GCC's science advisers was that "Lindzen's hypothesis that any warming would create more rain which would cool and dry the upper troposphere did offer a mechanism for balancing the effect of increased greenhouse gases. However, the data supporting this hypothesis is weak, and even Lindzen has stopped presenting it as an alternative to the conventional model of climate change."

Skeptic Assertion
Data suggests that changing solar activity is solidly influencing the global climate, effectually causing the world to get warmer. In 2005, the BBC cited a study that showed the sun was more active over the past 60 years than anytime in the previous 1150 years." Moreover, warmer temperatures have coincided with a steady increase in the number of sunspots over the past few hundred years.

The the GCC's own science advisers summarized the argument in 1995 as being that "Solar radiation is the driver for the climate system. Any change in the intensity of the solar radiation reaching the Earth will affect temperature and other climate parameters. Dr Robert Jastrow, Director of the Mt. Wilson Observatory, and others have shown a close correlation between various sun spot parameters, which they believe are a measure of solar intensity, and global average temperature for the past 120 years, the period for which reasonable quality data exist for both sun spots and global average temperature. The correlation has been pushed back to about 1700 using less accurate data for both temperature and sun spots. In addition, observations of Sun- like stars indicate that they show the amount of variability in radiation intensity needed to account for recent changes in the Earth's climate. More recently, Tinsley and Heelis at the Univ. of Texas have proposed a mechanism by which changes in solar activity can impact on climate in by a mechanism other than the direct change in the intensity of solar radiation impacting on the Earth's atmosphere.

Rebuttal
The most commonly cited study by skeptics -- by Usokin, Schussler, Solanki and Mursula -- also found that the correlation between solar activity and temperature ended around 1975. At that point, temperatures rose while solar activity stayed level. This led them to conclude that, “during these last 30 years the solar total irradiance, solar UV irradiance and cosmic ray flux has not shown any significant secular trend, so that at least this most recent warming episode must have another source.”

According to Skeptical Science -- a website by John Cook which reviews specific arguments used by the sceptics -- this is also confirmed by direct satellite measurements that find no rising trend since 1978, sunspot numbers which have leveled out since 1950 , the Max Planck Institute reconstruction that shows irradience has been steady since 1960 , and solar radio flux or flare activity which shows no rising trend over the past 30 years.

The GCC's own scientists noted that "Direct measures of the intensity of solar radiation over the past 15 years indicate a maximum variability of less than 0.1%, sufficient to account for no more than 0.1°C temperature change. This period of direct measurement included one complete 11 year sun spot cycle, which allowed the development of a correlation between solar intensity and the fraction of the Sun's surface covered by sun spots. Applying this correlation to sun spot data for the past 120 years indicates a maximum variability on solar intensity of 0.1%, corresponding to a maximum temperature change of 0.1°C, one-fifth of the temperature change observed during that period. ''If solar variability has accounted for 0.1°C temperature increase in the last 120 years, it is an interesting finding, but it does not allay concerns about future warming which could result from greenhouse gas emissions. Whatever contribution solar variability makes to climate change should be additive to the effect of greenhouse gas emissions.'' The Tinsley and Heelis proposed mechanism may revive the debate about the role of solar variability. To date is has not entered the climate change debate." (Emphasis added)

Skeptic Assertion
The climate has been naturally changing long before the Industrial Revolution and the human push of large quantities of carbon dioxide into the atmosphere, with the warming of several degrees often taking only centuries or even decades. For example, Europe was far warmer in the Middle Ages and far colder during the 17th and 18th century, causing a "Little Ice Age."

Rebuttal
John Cook, on his website Skeptical Science, states that "Natural climate change in the past proves that climate is sensitive to an energy imbalance. If the planet accumulates heat, global temperatures will go up. Currently, CO2 is imposing an energy imbalance due to the increased greenhouse effect. Past climate change actually provides evidence for our climate's sensitivity to CO2."

Skeptic Assertion
The idea that there is a scientific consensus supporting the idea that manmade carbon dioxide emissions are causing global warming is grossly inaccurate. According to The National Post’s series of articles profiling scientists who deny or are skeptical of anthropogenic climate change:

"“Many in the 'science is settled' camp claim that the skeptics are untrustworthy -- that they are either cranks or otherwise at the periphery of their profession, or that they are in the pockets of Exxon or other corporate interests. The skeptics are increasingly being called Deniers, a term used by analogy to the Holocaust, to convey the catastrophe that could befall mankind if action is not taken. Increasingly, too, the press is taking up the Denier theme, convincing the public that the global-warming debate is over.'"

Rebuttal
Naomi Oreskes, from the Department of History and Science Studies Program at the University of California, noted in an article in Science in 2004 that "The science consensus is clearly expressed in the reports of the Intergovernmental Panel on Climate Change (IPCC). Created in 1988 by the World Meteorological Organization and the United Nations Environment Programme, IPCC's purpose is to evaluate the state of climate science as a basis for informed policy action, primarily on the basis of peer-reviewed and published scientific literature. In its most recent assessment, IPCC states unequivocally that the consensus of scientific opinion is that Earth's climate is being affected by human activities...IPCC is not alone in its conclusions. In recent years, all major scientific bodies in the United States whose members' expertise bears directly on the matter have issued similar statements." The Academies of Science from 19 different countries all endorse the consensus. Eleven countries have signed a joint statement endorsing the consensus position. Additionally, the Academies of Science from another 8 countries also signed a joint statement endorsing the IPCC consensus.

Skeptics' Rebuttal
Oreskes' 2004 article on scientific consensus was immediately attacked as flawed. Benny Peiser repeated the same study and asserted that he found 34 peer-reviewed studies rejecting the opinion that Earth's climate is affected by human activities.

Rebuttal
However, a closer inspection shows that most did not reject the consensus at all, and Peiser has since retracted his criticism of Oreskes' study. The same argument was later made by the Viscount Monckton of Benchley, who showed five studies that he believed should be included in Oreskes' survey. However, two were reviews, not articles, and one was not peer-reviewed. A fourth reinforces the consensus opinion, and the fifth was updated by its author to affirm the impact of greenhouse gases on climate change in the past century.

Skeptic Assertion
The IPCC states that there are almost 150 billion tons of natural carbon dioxide emissions every year, which is almost 30 times the amount of carbon that humans emit.

Rebuttal
For approximately the last 10,000 years, until the industrial revolution, "every gigatonne of carbon going into the atmosphere was balanced by one coming out. What humans have done is alter one side of this cycle. We put approximately 6 gigatonnes of carbon into the air, but unlike nature, we are not taking any out…Since we began burning fossil fuels in earnest over 150 years ago, the atmospheric concentration that was relatively stable for the previous several thousand years has no risen by over 35%.”

Skeptic Assertion
Four global temperature measurement sets, the UK Hadley Climate Research Unit Temperature (HadCRUT), Remote Sensing Systems (RSS) of Santa Rose's Microwave Sounder Unit (MSU), University of Alabama-Huntsville lower troposphere data and the Goddard Institute for Space Studies (GISS) Land-Ocean Global temperature index data all showed that “January 2008 capped a 12 month period of global temperature drops on all of the major well-respected indicators,” showing significant cooling.

Rebuttal
Andrew C. Revkin wrote in the New York Times that “According to a host of climate experts, including some who question the extent and risks of global warming, it is mostly good old-fashioned weather, along with a cold kick from the tropical Pacific Ocean, which is in its La Niña phase for a few more months, a year after it was in the opposite warm El Niño pattern.” Moreover, “many scientists also say that the cool spell in no way undermines the enormous body of evidence pointing to a warming world with disrupted weather patterns, less ice and rising seas should heat-trapping greenhouse gases from burning fossil fuels and forests continue to accumulate in the air.” Similar drops occurred in 1988, 1991-92, and 1998, but the long-term warming trend remains clear. Additionally, “interviews and e-mail exchanges with half a dozen polar climate and ice experts…produced a rough consensus: Even with the extensive refreezing of Arctic waters in the deep chill of the sunless boreal winter, the fresh-formed ice remains far thinner than the yards-thick, years-old ice that dominated the region until the 1990s.”

Skeptic Assertion
Temperature change always precedes changes in carbon dioxide by several hundred years; thus, temperature drives carbon dioxide, not the other way round.

Rebuttal
According to Grist, “it is misleading to say that temperature rose and then, hundreds of years later, CO2 rose. These warming periods lasted for 5,000 to 10,000 years…so for the majority of that time (90% and more), temperature and CO2 rose together.” More specifically, “changes in orbital parameters (the Milankovich and other cycles) caused greater amounts of summer sunlight to fall in the northern hemisphere. This is a small forcing, but it caused ice to retreat in the north, which changed the albedo. This change -- reducing the amount of white, reflective ice surface -- led to further warmth, in a feedback effect. Some number of centuries after that process started, CO2 concentrations in the atmosphere began to rise, which amplified the warming trend even further as an additional feedback mechanism.”

Skeptic Assertion
The official temperature records of the Climate Research Unit at the University of East Anglia show that for the eight-year period between 1998-2005, global average temperature did not increase. This period of stasis exemplifies the “dynamic, fluctuating nature of climate change.”

Rebuttal
Research by Robert Fawcett "examines the temperature data of three different data-sets to determine the long term trend amidst the short term variations." He wrote in the Bulletin of the Australian Meteorological and Oceanographic Society that "short-term warming or cooling is expected from natural variability…and is not necessarily indicative of external influences." Research concluded that all three data sets demonstrate that the hot 1998 was due to the strong El Niño, and the trend from 1998 to 2007 is that of warming.

Skeptics’ Assertion
Using data from a network of deep-diving Argo buoys, scientists John Lyman, Josh Willis and Gregory Johnson showed in their 2006 study, “Recent Cooling of the Upper Ocean,” that there has been no warming in the upper ocean since 2004. These findings, say some global warming skeptics, are inconsistent with predictions of long-term global climate change.

Rebuttal
After their research on short-term ocean cooling was used as a reason to question global warming, Dr. Willis wrote a column for Canada’s National Post, describing how the Argo data does not contradict climate models. Willis wrote, “It is a well-established fact that human activities are heating up the planet and that global temperatures will continue to rise for decades to come…[F]our years with no warming in the upper ocean does not erase the 50 years of warming we’ve seen since ocean temperature measurements became widespread…[M}odels and datas of all different types tell the same story about the past century: the oceans are warming, sea levels are rising, the temperature of the atmosphere is increasing and carbon dioxide levels continue to go up.” Moreover, Lyman, Willis and Johnson, along with John Gilson, updated their results in “Correction to ‘Recent Cooling of the Upper Ocean,’” which showed that the cooling trend had been exaggerated and systematic measurement biases showed a spurious cooling trend since 2003.

Skeptics' Assertion
Michael Mann’s ‘hockey stick’ graph, which showed the results of a study of 112 proxy studies (tree rings, isotopes in ice, and other markers of relative temperature), was the main visual basis for the claim that the steepest temperature rise of the last thousand years occurred after the Industrial Revolution. However, two Canadian investigators, McKitrick and McIntye, re-did the study using Mann’s data and methods and found dozens of errors. When they corrected the errors, their research revealed sharply different results. Moreover, wrote Michael Crichton, “Mann and his associates used a non-standard formula to analyze his data, and this particular formula will turn anything into a hockey stick—including trendless data generated by a computer.”

Rebuttal
Since 1998, there have been at least ten proxy studies, analyzing different markers of relative temperature (corals, stalagmites, tree rings, ice cores, boreholes, etc.). The National Academy of Science released a summation of these various studies, which all conveyed “a qualitatively consistent picture of temperature changes over the last 1,100 years and especially over the last 400” and showed that “the instrumentally measured warming of about 0.6 degrees Celsius during the 20th century is also reflected in borehole temperature measurements, the retreat of glaciers, and other observational evidence, and can be simulated with climate models.”

The hockey stick graph, which “attracted considerable attention because the authors conclude that the Northern Hemisphere was warmer during the late 20th century than at any other time during the past millennium,” has been used as leverage by global warming skeptics because of controversy surrounding the methodologies and data that were used. Additionally, “the hockey-stick shaped curve became a symbol for the IPCC, and criticizing this particular data analysis became an avenue for some to question the credibility of the IPCC.” However, this denigrates the fact that the conclusion by Mann “has since been supported further by every single one of close to a dozen new reconstructions” and that “the prominent paper of von Storch and others, which claimed (based on a model test) that the method of [Mann and associates] systematically underestimated variability ‘was itself based on incorrect implementation of the reconstruction procedure.’” Furthermore, “the [possible rise in global temperature to 2100] range given by the IPCC did not use the reconstruction of [Mann] or any other proxy records of the past millennium.”

Skpetics claim
The GCC's own science advisers summarized the argument in 1995 as being that "The temperature record of the last 120 years cannot be explained by greenhouse gas emissions, which rose steadily through that period If greenhouse gases were the explanation for recent climate, one would have expected temperature also to have risen steadily through the period However, temperature rose from 1870 to 1930, then the leveled off to 1940, dropped between 1940 and 1970, and has been rising since 1970. Satellite measurements covering over 98% of the globe indicate that global average temperature has decreased slightly over the past 15 years, during a time when land based temperature measurements indicated a series of record high temperatures."

The GCC's advisers also noted another argument used by the "contrarians" was that "detailed temperature records do not agree with predictions about greenhouse warming. Prof Patrick Michaels of the University of Virginia presented a series of hypotheses about how greenhouse warming should affect temperature. Only two will be discussed in detail." They continued:


 * "First, if greenhouse gases were responsible for the increase in global average temperature, one would expect daytime maximum temperatures to increase. What is actually happening is that daytime maximum temperatures are staying constant, while nighttime temperatures are increasing. Michaels argues that the increase in nighttime temperatures is due to the urban heat island effect."


 * "Second, one would also expect Northern Hemisphere temperatures to have increased more than Southern Hemisphere temperatures, since greenhouse gas concentrations are higher in the Northern Hemisphere. However, Southern Hemisphere temperatures have increased more than Northern Hemisphere temperatures. Michaels argues that the smaller increase in the Northern Hemisphere is due to cooling by aerosols, a position which is now becoming generally accepted."

Rebuttal
The GCCC's own science advisers stated that "while atmospheric concentrations of greenhouse gases have risen steadily since 1870, their total increase has been too small for greenhouse warming to be distinguishable above the cooling effect of aerosols and the variability caused by all of the other factors which affect climate (volcanic eruptions, solar variability, random variability possibly due to the chaotic nature of climate, etc.). .This does not mean that a further increase in greenhouse gas concentrations will not add to measurable warming. Satellites measure the average temperature of a column of air from the surface to about 6 km, above the surface, while the land based measurements are surface measurements. Also, the land-based measurements are for land only. The oceans, which cover 70% of the Earth's surface, are not included. The oceans would be expected to warm more slowly than the land surface, lowering global average temperature."

"While raw data from the satellite measurements indicate a cooling of O.06°C/decade, correcting the raw data for known effects (volcanos and periodic warming of the Eastern tropical Pacific Ocean as part of the EI Nino cycle), yields 0.09°C/decade warming. The corrected satellite measurements still do not agree with the land-based temperature record, but they both show warming," they concluded.

As for Michaels argument, the GCC's own scientific advisers stated that "while some scientists argue that greenhouse warming has already occurred, most say that it cannot be separated from all of the other factors affecting climate, including the urban heat island effect and aerosol cooling. Thus, the fact that the recent temperature record does not agree in detail with a greenhouse gas warming scenario does not diminish the potential threat from substantially higher atmospheric concentrations of greenhouse gases."

Skeptics’ Assertion
Studies show that Mars, Neptune, Jupiter, Triton and Pluto are all warming: NASA shows that the Martian South Pole’s ice cap has been shrinking for three summers in a row, a new storm and a new red storm on Jupiter strongly suggests temperature change, a new study suggested that the brightening of Neptune correlates with the Earth’s temperature, and MIT research found that Pluto is experiencing global warming (as evidenced by a three-fold increase in the planet’s atmospheric pressure during the last 14 years) and that Neptune’s moon, Triton, is also experiencing warming that is causing part of its surface of frozen nitrogen to turn into gas. Fred Thompson in 2007 said these trends have “led some people, not necessarily scientists, to wonder if Mars and Jupiter, non-signatories to the Kyoto Treaty, are actually inhabited by alien SUV-driving industrialists who run their air-conditioning at 60 degrees and refuse to recycle.” Global warming skeptics say this interplanetary warming strongly points towards the sun or some other cosmic force being the cause of the recent global warming on Earth.

Rebuttal
There are several major flaws in the skeptic’s assertion. First, only 6 planets or moons out of the over hundred bodies in the solar system to have experienced observed warming; notably, Uranus is cooling. Additionally, solar activity is not increasing, confirmed by direct satellite measurements that find no rising trend since 1978, sunspot numbers which have leveled out since 1950, the Max Planck Institute reconstruction that shows irradience has been steady since 1960 , and solar radio flux or flare activity which shows no rising trend over the past 30 years. . Moreover, climate change on the other planets is fairly understood: Mars’ climate is primarily driven by dust and albedo, not solar variations, and there is little empirical evidence that Mars is warming;, Neptune’s orbit is 164 years so current brightening is a seasonal response, Triton’s warming is due to the moon approaching an extreme southern summer, and Jupiter’s storms are fueled by the planet’s own internal heat.

Related SourceWatch Articles

 * Climate change skeptics
 * International Conference on Climate Change (2008)
 * International Conference on Climate Change (2009)
 * SourceWatch:Project:Creating Articles on Sponsors and Speakers at The 2008 International Conference on Climate Change

External resources

 * John Cook's Skeptical Science compendium of doubter claims vs. what the science says
 * Coby Beck's How to talk to a climate skeptic compendium of delayer claims, science-related and otherwise
 * Tim Lambert's 2005 Global Warming Skeptic Bingo (of talking points plus links to refutations)